This invention relates generally to systems for detecting failures in machining processes. More particularly, this invention relates to equipment and methods for detecting stuck tools in automated machining operations.
Manufacturers use various machines to drill, bore, tap, and shape workpieces into final products. A particular machine may perform a single machining operation, such as drilling or tapping, or may perform a combination of machining operations. In a typical manual machining operation, an operator may secure a workpiece in a jig, or locating and clamping device, and then position the workpiece adjacent to the head portion of the machine. A toolxe2x80x94e.g., a drill bitxe2x80x94then engages the workpiece piece and performs its particular machining operationxe2x80x94e.g., drilling. When finished, the tool is retracted from the workpiece and returned to its starting position in the head portion of the machine. Prior to moving or repositioning the workpiece, the operator is able to determine whether the tool is stuck in the workpiece.
In an automated machining process, several machining operations are commonly performed in tandem by the same machine or multiple machines. Also, the actual machining of the workpiece may be carried at one or more machining stations that comprise the machining process. Initially an operator, robotic device, or other suitable means secures the workpiece to a travelling pallet (sometimes referred to a jig), or to a locating and clamping device at a machining station.
Typically, when the workpiece is secured to a travelling pallet, or jig, both the traveling pallet and workpiece travel together through the machining process. In another commonly used machining process, the workpiece travels by itself through the machining process. In this case, the workpiece cooperatively encounters stationary locating and clamping devices that will secure the workpiece at each machining station in the machining process. When the particular machining operation is complete, the locating and clamping devices, that secured the workpiece, remain at the machining station while the workpiece advances to the next machining station. Those of skill in the art will recognize other ways to secure the workpiece for machining are also available. For example, a combination of the two methods just described may be used to secure the workpiece.
A microprocessor-based system then moves the secured workpiece through the automated machining process. The secured workpiece is positioned adjacent to the head of a machine. One or more tools extend from the head towards the workpiece in order to perform work on or to machine the workpiece.
When a machining operation is completed, the tools retract from the workpiece and return to their starting position within the head. Depending on the machine used, the tools may be completely or partially within the machine head in their starting positions. The microprocessor-based system then moves the workpiece being worked on to another machining station or repositions it for another machining operation on the same machine or machining station. When the automated machining process is completed, the workpiece is removed from the moving pallet or stationary clamping device.
Stuck tools are a major problem in automated machining processes. A stuck tool is a tool that has become imbedded in the workpiece when the machining operation is completed. In this state, the stuck tools are usually broken-i.e., the tool has separated from the head even though part of it may extend into the head. However, a stuck tool does not have to be broken. The tool may remain attached to the head for many reasons. In this case, the head, tool, and workpiece are connected to each other.
In addition, broken tools are not always stuck in the workpiece. A broken tool may be retracted or pushed into the head. A broken tool may fall out of the head. Also, some tools break into many pieces and fall to the ground.
Typically, a stuck tool extends out of the workpiece and into the head. If the workpiece is then moved, which usually is the next step in an automated machining process, the stuck tool will most likely rip apart the head, the workpiece, and surrounding equipment. The expense of repairing or replacing damaged equipment is significant. The production loss is even more costly in this scenario.
The prior art provides many devices for detecting broken tools. Some are acoustic devices for measuring the change in frequency of the tool or measuring the change in vibrations within the workpiece when the tool breaks. Some detectors are fluid based devices; they leak water or air when the tool breaks. Other detectors are electrical and measure changing electrical parameters. Some detectors use clutches or other mechanical devices to measure the speed and other changes when a tool breaks.
While these prior art devices may detect a broken tool, they are not well suited for detecting a stuck tool. They do not determine whether a tool is imbedded in the workpiece. It is noted that a tool may be broken but not imbedded in the workpiece. While it is good to know a tool is broken, it is very important to know whether the tool is stuck in the workpiece. Moreover, a broken tool detector does not detect when an unbroken tool is stuck in the workpiece. In this case, a broken tool detector would indicate everything is fine, permitting the workpiece to move and thus wreak havoc on the equipment.
Accordingly, there is a need in automated machining processes to be able to detect a stuck tool prior to movement of the workpiece to the next or subsequent machining operation.
The present invention provides an apparatus and method for detecting stuck tools in automated machining operations. There is provided a stuck tool detector for use in an automated machining process having an automated machining tool with reciprocating tools for work on a workpiece. The stuck tool detector is comprised of at least one stuck tool sensing member that selectively travels in a plane of separation between the workpiece and the automated machine. There is also at least one stuck tool sensor that is cooperatively connected to a corresponding stuck tool sensing member such that the stuck stool sensing member will actuate a corresponding stuck tool sensor when a stuck tool is encountered resulting in an alarm signal.
The stuck stool sensing member travel is controlled by the automated machining tool which uses a microprocessor based controller, and can travel in a vertical, horizontal, radial or angled direction. The stuck tool sensing member can be a trip-wire, a blade, a moveable guide member, an electromagnetic wave, a light beam, or a laser beam. The trip-wire can further be a slat, a wire, or a cord, while the moveable guide member can be made of metal, plastic, composite materials, or an engineered elastomer.
In operation, the machining tool is retracted from the workpiece at the completion of a machining operation. Prior to moving the workpiece to a subsequent machining operation, the stuck tool detector is actuated to determine whether there is a stuck tool between the workpiece and the machine head. If a stuck tool is present, the stuck stool detector will generate an alarm signal that will alert the operator of a stuck tool. Alternatively or additionally, the microprocessor based system may receive and sense the stuck tool sensor alarm signal and take the appropriate action to prevent the automated machining process from proceeding to the next machining operation and thereby damaging the workpiece and machining tool.
In a first embodiment, the stuck tool detector has a detector arm that has a first end and a second distal end. There is also a trip-wire that is attached between the first end and second distal end of the detector arms. The trip-wire is further attached to a stuck tool sensor. The stuck tool detector rotates about a rotating pivot pin to move the trip-wire along a plane of separation between the workpiece and the head.
In a second embodiment, a blade, or moveable guide member, is cooperatively positioned between a first and second guide, or blade guide, for sliding the moveable guide member or blade along a plane of separation between the workpiece and the head. At least one proximity sensor is positioned adjacent to one of the blade guides to determine the position of the blade. Alternatively, a stuck tool sensor may be used to sense when the moveable guide member has stopped moving due to a stuck tool.
In a third embodiment, a detector transport, moves a moveable guide member, or blade, along the plane of separation between the workpiece and the machine head. Stuck tool sensors, such as an up-sensor and a down-sensor, determine the position of the detector transport and thereby the position of the moveable guide member.
There is also provided a method for detecting a stuck tool. First, a machining operation on a workpiece is completed. Next, the machine tool is retracted from the workpiece toward the machine. The workpiece and head are then held in place. The microprocessor based system then operates a stuck tool detector to determine whether there is a stuck tool in the workpiece. The stuck tool detector then generates a signal. The operator or microprocessor based system then carries out certain actions based on the stuck tool detector signal received. If the signal indicates that there is a stuck tool, the operator is alerted to the stuck tool by an alarm, or the machine may be shutdown. Other means or a combination may be used to alert the operator of the stuck tool. If there is no stuck tool, the workpiece moves to the next machining step.
The method and embodiments of the present invention can also detect multiple stuck tools. For example, the moving guide member, or blade, of the second and third embodiments may be configured for different or multiple tools. In addition, multiple moving guide members or trip-wires may be used. A fourth embodiment shows multiple, detector transports and moving guide member configurations. Furthermore, the stuck tool detectors may be positioned to pass the blade or wire through the plane of separation horizontally, vertically, or in some other orientation.
The following drawings and description set forth additional advantages and benefits of the invention. Other advantages and benefits will be obvious from the description and may be learned by practice of the invention.